This section provides background information related to the present disclosure which is not necessarily prior art.
Various industries use radio frequency (RF) to drive plasma chambers in order to fabricate various components such as integrated circuits, solar panels, compact disks (CDs), digital versatile (or video) discs (DVDs), and the like. Each fabrication process can vary depending upon the particular component being manufactured. The various processes often call for delivery of RF energy at varying frequencies, power levels, and efficiencies.
Present RF power delivery systems tend to be specifically tailored to the requirements of the particular plasma manufacturing process. RF power amplifiers and generators are thus not typically interchangeable or easily modified to accommodate various applications. Rather, each application typically has its own requirements, usually necessitating changing the RF power amplifier and/or the RF power generator.
In one example, some plasma manufacturing processes call for a power amplifier that operates in a mode characteristic of a class AB power amplifier. In a mode of operation characteristic of Class B operation, approximately half of the input wave cycle is amplified by a first switch, and the other half of the input wave cycle is amplified by a second switch operating in a complementary manner. Class AB operation is typically further exemplified by each device conducting a small amount during the portion of the cycle when it is generally off. This reduces the dead zone, or period when both devices are simultaneously substantially off, which minimizes or eliminates crossover. Class AB amplifiers typically trade off efficiency in favor of linearity and greater power output. In conventional power amplifiers, class AB efficiency is limited to about 70%.
Other manufacturing processes call for a power amplifier that operates in a mode characteristic of a Class E power amplifier. Class E operation is typically implemented using a switching power amplifier. Class E amplifiers are known to be arranged in a single ended configuration, as opposed to the push-pull configuration of Class AB amplifiers. For example, a switching device is connected at its output to a circuit having an inductor and capacitor in series (a serial LC circuit) connected to the load and connected to a supply voltage through a large inductance. In operation, the on state of a Class E amplifier occurs when voltage is at or near zero across the switch when high current is flowing through the switch element. The off state of a Class E amplifier occurs when the voltage across the switch is high and current flowing through the switch is at or near zero. That is, the switch acts as a low-resistance closed switch during the on part of the RF cycle, and acts as an open switch during the off part of the RF cycle. Class E amplifiers typically trade off power output in favor of efficiency and other benefits. Class E efficiency is typically at least 85% and can be as high as 95%. Typical Class E amplifiers are typically less stable into high voltage standing wave ratio (VSWR) load mismatches.
Returning to the RF plasma manufacturing process, manufacturers may have a need for a Class AB characteristic power amplifier to provide RF power for a plasma process for certain applications. The same manufacturer, in other applications, may require a Class E characteristic power amplifier to provide RF power for a different plasma process. The manufacturer prefers to achieve either Class AB or Class E characteristic operation from a single device in order to achieve flexibility and minimize costs. Manufacturers have not yet been able to meet this customer requirement.
Conventional power amplifiers include a network including a capacitor and an inductor at an output prior to connection to a load. Such networks may also include an additional capacitor and may be referred to as a CLC network. Power amplifier designers have typically used the CLC networks to shape or condition the output signal prior to application to the load. The CLC networks may also reject transients and out of band energy reflected back from the load. However, the use of such CLC networks has been limited to these applications, and other applications of the CLC network have not been considered.